1. Field of the Invention
The present invention relates to a workpiece supporting device supporting a workpiece machined by a tool on a machine tool and also relates to a seating mechanism using for a clamped body. Especially, the present invention relates to the workpiece supporting device and the seating mechanism therefor to detect precisely a clamping force and overload acting on the clamped body.
2. Description of the Related Art
It is typically known for a workpiece supporting device to equip a clamping mechanism or a fixing mechanism for a workpiece and to have in this mechanism a load sensor detecting a clamping force or a fixing force acting on said workpiece. These related art of the workpiece supporting device are disclosed in Japanese Patent Laid-open Publication Nos. 7-40200, 8-229762, 9-183033, 10-151537 and 11-320305. It is disclosed in Japanese Patent Laid-open Publication No. 7-24680 for a workpiece supporting device to mount a strain gage on a fixing shaft and to detect a deformation strain acting on the fixing shaft in order to detect a fixing force. In these related art of the workpiece detecting device, three or more seating sheet members are mounted on a base and the workpiece supporting device or the fixing device disclosed in these Publications clamps the workpiece by contacting a reference surface of the workpiece to the seating sheet member. It is needed for a high accuracy of a machining that the reference surface is maintained to contact to the sheet member with a predetermined force. Japanese Patent Laid-open Publication Nos. 7-40169 and 9-201742 disclose a related art of a seating detection means to detect leakage of hydraulic flow from a discharging port opened on a top surface of the sheet member by a pressure sensor in a hydraulic circuit in order to detect a seating of the reference surface of the workpiece on the sheet member.
In the above-mentioned related art of the workpiece supporting device, since the detection of the seating depends on the leakage of hydraulic flow between the sheet member and the reference surface of the workpiece, accumulation of a machined chip on the sheet member or an abrasion of the sheet member affect malfunction against the detecting accuracy so that it must require an additional protector for said malfunction. More over, the seating mechanism based on the leakage of hydraulic flow can detect only whether the seating is but can not detect whether the clamping or fixing force to maintain the seating is adequate. The above-mentioned related art of the workpiece supporting device must need the seating detection means in addition to the clamping mechanism or the fixing mechanism with the load sensor to guarantee the clamping or fixing status of the workpiece by the predetermined force to the sheet member. If a load sensor will be mounted in the sheet member the load sensing means and the seat sensing means will be performed by one means, however, since the load cell or the strain gage is functioned by elastic deformation of a sensing body by the clamping or fixing force, a reference position is displaced by the clamping or fixing force to raise a decrease of the machining accuracy. In order to perform the high accuracy, it is needed to detect the seating of the workpiece on the work table by a suitable clamping force.